Four Popular Coffee Myths, Debunked by Science

You crave it in the morning, you wait in long lines for it, and I’m drinking it while I write this: coffee is everywhere. But that means misinformation about it is everywhere too. Coffee doesn’t rob you of water, sober you up, or keep your children short, so let’s grind up these myths and brew a hot pot of truth.

Myth: Coffee Dehydrates You

The notion that coffee dehydrates you is a widespread misconception, much to the chagrin of waitstaff everywhere who are asked for “a coffee and a water” only to later clear a table of untouched water glasses. This concept originated because caffeine, a main ingredient in coffee, is a diuretic, or a substance that makes you go pee a lot. The logic seems sound; the more you pee, the more water your body is losing, right? But that logic is missing one important part of the whole “drinking coffee” formula: the water you’re drinking in the coffee.

The myth about coffee’s sobering powers is particularly important to debunk because the co-use of caffeine and alcohol could actually lead to poor decisions with disastrous outcomes. People who have consumed only alcohol, who feel tired and intoxicated, may be more likely to acknowledge that they are drunk. Conversely, people who have consumed both alcohol and caffeine may feel awake and competent enough to handle potentially harmful situations, such as driving while intoxicated or placing themselves in dangerous social situations.

So, what can you actually do to sober up? Drink water to keep yourself hydrated, eat some food to help slow the absorption of alcohol, and wait it out . There’s no magic elixir that will sober you up, and believing one exists is a potential danger to you and others.

Myth: Coffee Stunts Your Growth

You can blame the “coffee stunts your growth” myth on some clever advertising, believe it or not. It most likely started when Postum, a coffee alternative made from roasted wheat bran, wheat, and molasses, began a smear campaign at the turn of the 20th century denouncing coffee’s effects on people’s health, especially children. It worked. Ads (like the one above from 1933) terrified parents by telling them that coffee stunted their children’s growth and would make them jittery, nervous, and unable to learn in school. Postum’s cryptic slogan of “There’s a reason” certainly didn’t help.

The bottom line is there’s no evidence whatsoever that coffee stunts growth, and it’s unlikely that caffeine even affects bone health in anyone who isn’t already struggling to maintain it. That said, caffeine is a stimulant, and kids as well as adults should consume it in moderation. The U.S. doesn’t have any official guidelines for caffeine intake, but Health Canada has recommendations for kids, adults, and even pregnant women.

Myth: An Espresso Has More Caffeine Than a Cup of Coffee

If you’re comparing a shot of espresso to an average cup of coffee (about 8 oz. according to the National Coffee Association), that cup of joe actually packs way more of a jolt. As Coffee Chemistry explains, 8 oz. of black coffee has somewhere between 65-140 mg of caffeine (an average of 92.5 mg), and a typical 1 oz. espresso shot has somewhere between 30-50 mg (an average of 40 mg). So a serving of coffee has 2.3x as much caffeine as a serving of espresso, on average. That means when you order an americano at the coffee shop, make sure you’re only doing it for the flavor, because you’re not getting more caffeine. You’re probably getting less.

That said, if you were to compare them by volume, coffee only has 8-15 mg of caffeine per ounce, and espresso still averages 40 mg per ounce. But you’d probably never order a single, 8 oz. espresso, so it’s a moot point. The idea that espresso has more caffeine than regular coffee likely comes from the fact that espresso has a much darker roast, and there’s an assumption that the bolder taste of a darker roast correlates with higher caffeine content. This is also untrue.

24 Comments

You forgot the myth that coffee tastes good. I debunked that one years ago by trying it. I wish I liked coffee, but I just can’t. It’s a shame as I love coffee houses and the smell of coffee, but the taste is just terrible. And yes, you can tell me it’s an acquired test, but why would I want to drink something I don’t like until I finally get Stockholm Syndrome and start liking it?

Coffee is like wine, there are many varieties of it with various different tastes. Factor in different roasts and a multitute of preparation methods, and somewhere in this vast world might be a cup that is yours.

I was honestly the same way until I found a flavor I liked (I’m referring to black ground coffee). The Folgers stuff that my office brews is pretty bad, usually with a very burnt, rough flavor. The stuff I brew at home is way smoother and I cycle through caramel, mocha, and vanilla flavors. I see it similar to beer. If you drink crappy stuff, you’ll never like it unless you just keep drinking it and grow accustomed to it. But if you keep trying different varieties, you may come across one you like (which is different than acquiring the taste). Of course, you may just never like coffee.

I’m starting to get a little tired of my nutritionist. It’s been debunked over and over that coffee is not as much of a diuretic as once claimed. She even told me that tea - TEA - doesn’t count towards my water intake, and that has less than HALF as much caffeine as coffee. Plus it’s good for you, so I think its worth it regardless. I think it’s dangerous advice to say that it doesn’t count, because I’m already drinking 64oz a day which is what is recommended for my weight, and if you factor in 16oz of coffee and maybe 16oz of tea before bed? That’s a whole lot of liquids.

The last bit about espresso is quite false - caffeine content of a shot served to you in a cafe will vary wildly, from less than 60 mg per serving to over 200 mg per serving. This depends mainly on two factors: the coffee itself (i.e. is there any robusta included in the blend?), and the dose of coffee used. Generally speaking for any coffee brewing method, the higher the dose, the higher the caffeine content in the cup. If you use 20 grams for your shot of espresso but only 12 grams for your mug of coffee, the espresso is very likely to have more caffeine. For reference, check out some of the analyses on caffeine content in coffee and espresso, many of which are available for free through Google Scholar. This article shows how widely variable caffeine content can be for “an espresso,” as served to you in a cafe (54 - 317 mg). http://pubs.rsc.org/is/content/art… (Also, a nitpicky point on espresso as well: as it’s just a brewing method, you can use any coffee you like - light, dark, blend or not, doesn’t matter.)

Agree with everything you say here as well. I think roast level also contributes to caffeine content. Traditional espresso uses darker roasts while drip coffee is lighter. So there's another variable. But specialty coffee shops sometimes use the same roast level between drip and espresso if it just happens to brew right for both methods.

I had my first cup of coffee when I was 3 because my grandpa drank it daily and I wanted to be like grandpa. Everyone gave him shit because A. I was 3 and drinking black “military grade” coffee and B. It was going to “stunt” my growth. I was the tallest and biggest kid through all of elementary school, towering over even my teachers in the class photos and I maxed out at 6'4" Freshmen year of high school (it was like puberty stopped me from growing, I did all of my growing before puberty). 6'4" isn’t giant, but it is when you’re 13 years old. Everyone then switched to “jesus what are you feeding that kid?” to which I always replied “Coffee.” Coffee definitely does not “stunt your growth.”

I love the taste of coffee, but even a single cup gives me painful abdominal cramps and, eventually, the runs. You’d think it’s the caffeine, but I can take straight 200mg caffeine pills (or two) without similar impact. I’ve been told cold brew might be better on me. Any thoughts?

Cold-brew coffee has been, at least for me, a completely different animal. Virtually all hot-brew coffee I have to add both cream and sugar to in order to make palatable, but I drink the cold-brew I make black or with a tiny amount (1/8 tsp or less in a 15-ounce mug) of sweetener. Still, your problem may well be one of the other alkaloids in the coffee; remember that the coffee plant evolved to contain those compounds to make itself unpalatable so it wouldn’t get eaten.

Unfortunately for you, caffeine is not the only thing in coffee. You could be allergic or have an intolerance to any number of substances in it. An allergy specialist might be able to help you figure out exactly what it is—there are so many different kinds of coffee (and different preparations), there might be one that works for you.

Hangover “cures” make me lol. When I drank (many years ago) everyone had their cures or magical crap that would get rid of your hangover. NONE work as a cure. There’s some that help your body to re-hydrate and sure advil/ibuprofen can help a bit to reduce inflammation etc but the best “cure” is simply to eat and go to sleep. Period.

That said, if you were to compare them by volume, coffee only has 8-15 mg of caffeine per ounce, and espresso still averages 40 mg per ounce. But you’d probably never order a single, 8 oz. espresso, so it’s a moot point. Back in my college days, I worked at a coffee shop on campus and someone actually did try to order a large espresso and when I gave them a triple shot they clarified that they meant a large cup filled with espresso. So what I’m saying is you should rephrase that to “a reasonable person who understands what espresso is would never order a single 8oz serving” :)

The idea that espresso has more caffeine than regular coffee likely comes from the fact that espresso has a much darker roast, and there’s an assumption that the bolder taste of a darker roast correlates with higher caffeine content. Wait... what? You just finished saying that one ounce of espresso has nearly 3 times as much caffeine (40 mg/ounce) than coffee (8 - 15 mg/ounce). So wouldn’t the assumption that espresso contains more caffeine than coffee have more to do with that the fact that this is absolutely true, rather than the taste?

Yes, we all understand that a serving of coffee has more caffiene than a serving of espresso. If the simple question is “which has more caffiene” you have to compare equal amounts. The unequivocal answer is espresso has more caffeine. The way the paragraph is worded is confusing because it states that people assume there is more caffeine in espresso because of the bolder taste and darker roast. That’s not correct. The reason people think there is more caffeine in espresso is because there IS more caffeine in espresso.